Conventionally, vinyl addition polymers of cyclic olefins represented by norbornene polymers have been industrially used in the field of optical films and the like as an organic material being excellent in heat resistance and transparency. There have been various reports that such vinyl addition polymers of cyclic olefins can be produced by the addition polymerization of cyclic olefin monomer(s) using a catalyst containing transition metals such as Ti, Zr, Cr, Co, Ni and Pd.
For example, the European Patent Publication No. 0445755 (Patent Document 1) reports that a vinyl addition homopolymer of norbornene having the number average molecular weight exceeding 1,000,000 can be produced by polymerizing a norbornene monomer alone by using a transition metal compound of elements belonging to five to ten groups of the periodic table as a main catalyst and methylaluminoxane (MAO) as a cocatalyst. However, polymerization of norbornene containing polar group which has higher difficulty has not been conducted with this catalyst system, and in addition to concerns about the catalyst deactivation due to the influence of the polar group, the obtained polymer was not a monodisperse polymer wherein the molecular weight distribution (Mw/Mn) exceeds 2.5.
Meanwhile, U.S. Pat. No. 3,330,815 publication (Patent Document 2) discloses vinyl addition homopolymers of norbornene containing polar group and copolymers with norbornene. However, the patent has not reported an example where a polymer having a number average molecular weight exceeding 10,000. Also, the polymerization activity of the catalyst is low so that the production method was far from being an industrially useful method.
Moreover, Japanese Patent Publication No. 3678754 (WO96/37526; Patent Document 3) and JP-A-2008-31304 publication (Patent Document 4) disclose a method for improving an addition polymerization of a norbornene monomer alone containing polar group or copolymerization with norbornene. Though these methods improved both of polymerization activity and molecular weight of the obtained polymer, they only disclose copolymer having number average molecular weight less than 200,000 in examples and have not succeeded in producing copolymers having number average molecular weight of 200,000 or more which is required for various mechanical properties to be developed to a practical level. In Table 1 of Patent Document 4, the number average molecular weight (Mn) entries and the weight average molecular weight (Mw) entries replace each other. It is obvious from that Mw/Mn values should be around 2.5, and it is clear that a copolymer having a number average molecular weight exceeding 200,000 did not exist if data in Table 1 are interpreted properly.
Contrary to these methods, International publication No. WO06/064814 (EP 1826221; Patent Document 5) discloses that addition copolymerization of norbornene containing polar group and norbornene can be efficiently performed by using compounds of transition metals belonging to eighth to tenth groups of the periodic table as a main catalyst in combination with a cocatalyst capable of producing a cationic transition metal compound through the reaction with the main catalyst to thereby obtain copolymers having high molecular weight. However, the norbornene compound disclosed by the publication has a structure wherein an ester group is directly introduced into a norbornene skeleton, and since the distance between the carbon-carbon double bonding site and the polar group is short, the norbornene compound easily forms coordinate bonding with a transition metal complex as a catalyst, resulting in catalyst deactivation. Accordingly, the method enables producing a polymer having high activity and high molecular weight in addition polymerization of a norbornene monomer alone. However, in case of using a norbornene compound having a polar group, a copolymer having high molecular weight can be obtained but the catalyst activity of the copolymer was low.
From the description of these prior art documents, it can be seen that a high-activity catalyst system capable of obtaining a copolymer having a number average molecular weight as high as 200,000 or more in addition copolymerization of a norbornene compound containing a polar group, which system experiences little deactivation even when a norbornene compound containing a polar group was used, was previously unknown.
As discussed above, in a method for producing addition copolymers of norbornene containing a polar group, there have been no previous cases making it available to combine a high activity catalyst and a norbornene compound having a polar group to thereby obtain a copolymer having practical mechanical properties. Consequently, a method for sufficiently producing a copolymer which can be developed for practical by finding out an appropriate combination of a high activity catalyst and a norbornene compound containing a polar group has been demanded.